Do not perform strength reduction x - x => 0 between numeric litera…

…ls (address #16)

Constant folding will resolve this on its next visit by executing the operation instead of direct substitution

src/muqsit/arithmexp/expression/optimizer/OperatorStrengthReductionExpressionOptimizer.php

@@ -31,12 +31,14 @@
 
 final class OperatorStrengthReductionExpressionOptimizer implements ExpressionOptimizer{
 
+	private PatternMatcher $any_non_numeric_matcher;
 	private PatternMatcher $binary_operation_matcher;
 	private PatternMatcher $unary_operation_matcher;
 	private PatternMatcher $multiplication_operation_matcher;
 	private PatternMatcher $exponentiation_operation_matcher;
 
 	public function __construct(){
+		$this->any_non_numeric_matcher = Pattern::not(Pattern::instanceof(NumericLiteralExpressionToken::class));
 		$this->binary_operation_matcher = new ArrayPatternMatcher([
 			AnyPatternMatcher::instance(),
 			AnyPatternMatcher::instance(),
@@ -207,7 +209,7 @@ private function processBinaryExpression(Parser $parser, Expression $expression,
 				default => $this->processAddition($parser, $operator_token, $left, $right)
 			},
 			"-" => match(true){
-				$this->tokensEqualByReturnValue($left, $right) => [new NumericLiteralExpressionToken(Util::positionContainingExpressionTokens([...$left, ...$right]), 0)],
+				$this->tokensEqualByReturnValue($left, $right) && $this->any_non_numeric_matcher->matches([...$left, ...$right]) => [new NumericLiteralExpressionToken(Util::positionContainingExpressionTokens([...$left, ...$right]), 0)],
 				$this->valueEquals($left, 0) => [
 					new NumericLiteralEXpressionToken(Util::positionContainingExpressionTokens($right), -1),
 					...$right,

tests/muqsit/arithmexp/OptimizerTest.php

@@ -324,6 +324,12 @@ public function testSubtractionOperatorStrengthReductionForEqualOperands() : voi
 		self::assertEquals(0, $expression->evaluate());
 	}
 
+	public function testSubtractionOperatorStrengthReductionForEqualOperandsYieldingNaN() : void{
+		$expression = $this->parser->parse("inf - inf");
+		self::assertInstanceOf(ConstantExpression::class, $expression);
+		self::assertNan($expression->evaluate());
+	}
+
 	public function testSubtractionOperatorStrengthReductionForEqualOperandsWithGrouping() : void{
 		$expression = $this->parser->parse("(x * y * z) - (x * y * z)");
 		self::assertInstanceOf(ConstantExpression::class, $expression);